Question: Simplify the following expression: $\sqrt{90} - \sqrt{40}$
Explanation: First, try to factor any perfect squares out of the radicals. $= \sqrt{90} - \sqrt{40}$ $= \sqrt{9 \cdot 10} - \sqrt{4 \cdot 10}$ Separate the radicals and simplify. $= \sqrt{9} \cdot \sqrt{10} - \sqrt{4} \cdot \sqrt{10}$ $= 3\sqrt{10} - 2\sqrt{10}$ Finally, simplify by combining the terms. $= ( 3 - 2 )\sqrt{10} = \sqrt{10}$